1. Field of the Invention
The present invention relates to a staple driver which is adapted to be mounted in a stapler for driving staples into a sheaf of papers to eject a U-shaped staple and drive its legs through the sheaf of papers in a striking motion, the striking motion being directed perpendicular to the web portion of the staple, said driver having a plate-shaped portion with an edge surface whose width is essentially equal to the thickness of the staple and which is arranged, in the striking motion, to be applied and pressed against the web portion of the staple.
2. Description of Related Art
In prior-art staplers, use is made of a magazine which either contains straight wire staple blanks which are juxtaposed and releasably interconnected to form a strip of staple blanks, or contains U-shaped staples which are arranged closely together in a long row. In the former case, the stapler has a shaper as well as a driver. As stapling is carried out by means of the stapler, the strip of staple blanks is advanced step by the step to the shaper which in a striking motion shapes the straight staple blank, which is in a shaping position, to a U-shaped staple. This U-shaped staple is advanced by the step-by-step advancing of the strip to a driving position in front of the driver, which in a striking motion releases the staple from the strip and drives its legs into a sheaf of papers. In the latter case, i.e. when the magazine contains U-shaped staples, shaping need, of course, not take place. The stapler then has no shaper but a driver which operates in the fashion described above.
A prior-art driver and the manner in which it drives a U-shaped staple into a sheaf of papers will now be described with reference to FIGS. 1A-1F.
FIGS. 1A-1F show a portion of a staple driver 1 which consists of a metal plate having essentially the same thickness as the U-shaped staple 2 which is to be driven into a sheaf of papers 3. The driver 1 is arranged in a stapler (not shown) reciprocating in the direction of the double arrow P1.
The staple driver 1 has at its side edges projections 4 projecting in the direction of the staple 2. The projections 4 are pointed and each located in front of one of the two legs 2xe2x80x3 of the staple 2 arranged in the driving position, so as to engage with the web portion 2xe2x80x2 of the staple 2 in front of the legs 2xe2x80x3 as the staple 2 is being driven in. The driver 1 also has a portion 5 located between the projections 4 and having an edge surface 6 facing the staple 2.
The stapler also has a clinching mechanism which comprises two clinching means 7 each of which is turnable on a pivot 8 which is perpendicular to the plane of the staple 2, and each of which is arranged to cooperate with a leg 2xe2x80x3 of the staple 2.
When the staple driver 1 in a striking motion is moved in the direction of the staple 2, its two pointed projections 4 will engage with the web portion 2xe2x80x2 of the staple 2 in front of the legs 2xe2x80x3. The projections 4 bite into the web portion 2xe2x80x2, the edge surface 6 of the portion 5 of the driver 1 being applied and pressed against the web portion 2xe2x80x2 in order to drive, during the continued striking motion of the driver 1, the legs 2xe2x80x3 through the sheaf of papers 3 until the web portion 2xe2x80x2 comes into abutment against the upper side thereof (see FIG. 1C). When the staple legs 2xe2x80x3 are driven through the sheaf of papers 3, they strike against the clinching means 7 arranged in a first turning position and are bent slightly towards each other (see FIG. 1C). The driver 1 is retained in the position shown in FIG. 1C, and the clinching means 7 are turned to a second turning position (FIG. 1D) while they bend the staple legs 2xe2x80x3 further into abutment against the underside of the sheaf of papers 3, i.e. to a position in which the legs 2xe2x80x3 extend parallel with the sheaf of papers 3. Subsequently the clinching means 7 are turned back to the first turning position while the driver 1 is retained in its position with the edge surface 6 pressed against the web portion 2xe2x80x2 of the staple 2 (FIG. 1E). Finally, the driver 1 is returned to its starting position shown in FIGS. 1A and 1F.
When the staple 2, as is usually the case, is made of a metal wire, it can, after completion of driving and clinching, be deformed somewhat in that the staple legs 2xe2x80x3 spring out a distance from the underside of the sheaf of papers 3 in the manner shown in FIG. 1F. This results in the staple 2 obtaining a considerably greater thickness, seen in the driving direction of the staple, than in the clinched position shown in FIG. 1E. This increase in thickness is of course not desirable. For instance, it causes trouble when a plurality of sheaves of an arbitrary number of stapled sheets of paper are inserted in a file since the thickness of the entire sheaf will be considerably much greater in the upper left corner where the staples are usually arranged when stapling together sheets of paper. Moreover, there is a great risk of the user being torn by the projecting leg ends.
The object of the present invention is to provide, in view of that stated above, a staple driver which eliminates the above problems caused by the resilience properties of the staple material.
According to the invention, this object is achieved by a staple driver, which is of the type mentioned by way of introduction, being given the distinctive features defined in claim 1, i.e. that in combination with the feature known per se that the staple driver has pointed projections which are arranged to engage, in the striking motion, with the web portion of the staple in front of the legs of the staple, it has the feature that the edge surface in its longitudinal direction extends along an outwardly curved arc.
The edge surface preferably is of essentially the same length as the web portion of the staple and is preferably arcuate over its entire length.